Patterned media with an alternating series of concentric servo zones and overlap zones

ABSTRACT

Embodiments described herein provide for patterned media concentric zones with an alternating series of concentric servo zones and overlap zones. The overlap zones facilitate the writing of servo data between servo zones of different servo frequency. The overlap zones may be dual frequency zones. The dual frequency zones have a first set of overlap patterns with the substantially identical pattern as the bordering lower frequency servo zone and a second set of overlap patterns with the substantially identical pattern as the bordering higher frequency servo zone. A bootstrap zone can be included near the inner diameter to assist initial servo writing. Alternatively the overlap zones are bootstrap zones. Such bootstrap zones have both bootstrap patterns and overlap patterns, the overlap patterns have the substantially identical pattern as a bordering servo zone. Bootstrap patterns only require DC magnetization for servo operability.

FIELD OF THE INVENTION

The invention relates to the field of disk drive systems and, inparticular, to servo patterns imprinted on a patterned magnetic disk toalign a slider with data on the magnetic disk.

BACKGROUND

Many computing systems use disk drive system systems for mass storage ofinformation. Magnetic disk drives typically include one or more slidersthat include a read head and a write head. An actuator/suspension armholds the slider above a magnetic disk. The magnetic disk includes dataregions and servo sectors. A voice coil motor (“VCM”) moves theactuator/suspension arm to position the slider over selectedmagnetically written data with the feedback of servo data. Electronicson the disk drive system include a write driver, a read signalpreamplifier, a read-write channel, a controller, and firmware. Thecontroller typically is an assortment of circuit chips connected on aprinted circuit board. The controller includes one or moremicroprocessors, memory, servo control circuits, hard disk controlcircuits, spindle motor drivers, and VCM drivers. The read-write channelcan include analog to digital conversion circuits, data clocks, servoclocks, and phase locked loops.

Both the data regions and servo sectors can include information that ismagnetically written by the write head onto the magnetic disk and alsoread back by the read head from the magnetic disk. The data regionsinclude data tracks that are available to store end-user files and diskdrive system parameter data (or maintenance data). The data is writtentypically in 512 byte or 4 kilobyte data blocks. Each data block usuallyhas a data sync field, the actual data (typically encoded and possiblyencrypted), and error correction data. The end-user is free to store newdata and later modify the data.

The servo sectors include servo data that is used to position theslider. Servo data is typically only written at the manufacturingfacility and cannot be changed by the end-user. There are varioustechniques for writing servo data on a magnetic disk; in a typicalmethod called self-servo writing the servo data is step-wise propagatedfrom the inner diameter to the outer diameter using the write head towrite servo data that is later used for servo track following to assistthe writing of additional servo data. One complicating factor forself-servo writing (as well as normal data writing) is the radialread-write offset length (“RWO”) between the write head and the readhead. The RWO changes with the slider's angular position over themagnetic disk based on the location of the read head and write head onthe slider and the arc made by the actuator over the magnetic disk.Often in self-servo writing, the read head is offset toward the innerdiameter from the write head and the servo data is written from theinner diameter to the outer diameter.

FIGS. 18A-18C illustrate a close-up view of a slider's 122 variableangular position over a magnetic disk. As mentioned, the slider 122 isconfigured with a read head 130 and a write head 140 that are operableto read from and write to the magnetic disk. When the slider 122 ispositioned towards the inner diameter of the magnetic disk, the RWO 900between the read head 130 and the write head 140 is at its smallestdimension relative to the magnetic disk. As the slider 122 moves to thecenter of the magnetic disk, the RWO increases (RWO 901 of FIG. 18B),reaching its maximum RWO (902) at the outer diameter of the magneticdisk in FIG. 18C.

Servo data may include a synchronization field (servo sync), a sectoraddress mark (“SAM”), sector-ID, track-ID (sometimes called thecylinder-ID), a servo burst, a repeatable runout (“RRO”) value, and apad. Data tracks are usually identified by a combination of thetrack-ID, servo burst, and/or RRO value.

The servo sync is typically the first servo data read by the read headas it passes through a servo sector. The servo sync can be used by theread-write channel to establish servo frequency and servo clock phase.Portions of the servo sync can also be used for automatic gain controlin the disk drive system electronics. The servo sync can be written witheither a single magnetic polarity or with an alternating polarity asdemonstrated in U.S. Patent Application Pub. No. 2006/0279871A1. Theservo sync is sometimes referred to as a preamble.

The servo frequency in conventional disk drive systems is constant fromthe inner diameter to the outer diameter of the magnetic disk. As aresult of this constant frequency, the servo sectors increase incircumferential length proportional to radial location. For instance,the circumferential length of the servo sector at the outer diameter ofthe magnetic disk may be about twice the length of the servo sector atthe inner diameter.

If a zoned servo architecture is employed, the servo frequency increasesbetween servo zones from the inner diameter of the magnetic disk to theouter diameter. The servo frequency changes between the zones roughlywith the mean radius of each servo zone. The servo frequency within eachzone usually remains constant. Because the servo sector is broken intoshorter radial servo zones, the circumferential length of the servosectors does not vary as much as in the conventional servo design. Thereduced variance in circumferential length when using zoned servoprovides an advantage when using patterned media as the servo patternsfor zoned servo can be more uniform in circumferential length from theinner diameter of the magnetic disk to the outer diameter. See U.S.patent application Ser. No. 12/699,581 (“the '581”) and the descriptionbelow of Dry Planarization Design Rules #1 and #2.

Examples of zoned servo can be found in U.S. Pat. Nos. 6,178,056 FIGS.2B and 2C; 7,012,773 FIGS. 10, 15, 20, 28 and column 11 (“the '773”);and 7,715,138 FIG. 2A. The '773 FIG. 10 demonstrates a design with aseries of concentric zones making up an alternating series of normalservo zones that are single frequency (“servo zones”) and overlap zonesthat are dual frequency (“dual frequency zones”). In the dual frequencyzones, half of the servo sectors use a first servo frequency that is thesame as the bordering lower frequency servo zone while the remainingservo sectors use a second servo frequency that is the same as thebordering higher frequency servo zone. In the '773 FIG. 10 design, theservo zones and dual frequency zones are arranged in continuous radialservo sectors. FIGS. 15, 20, and 25 of the '773 demonstrate otherpossible zoned servo arrangements in which the servo sectors are notradially continuous.

The SAM (also called a servo address mark, start of servo mark, andservo sync byte) acts as a starting point from which to locate otherservo data. For instance, the track-ID, sector-ID, and servo burst canbe positioned a predefined distance from the SAM in a predefined order.The SAM is typically a unique magnetic shape so that it is more easilydistinguishable by the disk drive system electronics from other magneticinformation written on the magnetic disk. The SAM may not follow thesame rules or constraints as other data that is written on the magneticdisk. For instance, the SAM may be written at a different frequency orotherwise differ in width and/or spacing from the other servo data.

The sector-ID is used to identify the particular servo sector as theslider circles a track. A track may have 250 or more sequential servosectors. The sector-ID provides the controller with the circumferentialposition of the slider. The sector-ID is typically substantiallyidentical in each track of an individual servo sector as it propagatesradially from inner diameter to outer diameter. The sector-ID may be aunique digital number identifying the specific servo sector, such as asector-ID between one and 250 if there are 250 servo sectors in onetrack. The sector-ID may be split between several servo sectors toreduce the circumferential length of each servo sector; in this case,several servo sectors need to be read to determine the completesector-ID. In some designs, the magnetic disk has a start of track markand the controller includes a counter; in this case, a start of trackmark resets the counter and the counter is incremented each time new aSAM is encountered by the read head to provide a running count for thecomplete sector-ID. In this specification, the term sector-ID is meantto include each of these possible designs.

The track-IDs are used to identify the particular radial position as theslider moves radially from the inner diameter to outer diameter. Thetrack-ID is often written in a gray code digital format; there are manygray code formats and some formats encrypt the track-ID and/or provideerror-correction redundancy. The track-ID can also be written using aplurality of phase patterns (e.g., chevron patterns), as demonstrated inFIGS. 4A, 4B, 8, and 10 of U.S. patent application Ser. No. 12/634,240(“the '240”). The track-ID provides the controller with the radialposition of the slider. The track-IDs can ascend in numerical valuewithin a specific servo sector from inner diameter to outer diameter;the track-ID can be substantially identical within the sequential servosectors of a specific track. The track-ID may be a unique digital numberidentifying the specific radial position, such as a number between oneand 100,000 if there are 100,000 unique gray code numbers in the servosector from the inner diameter to the outer diameter. There is usuallynot a one to one correspondence between magnetically written data tracksand gray code track-IDs. The track-ID may also be split between severalservo sectors to reduce the circumferential length of the track-ID ineach servo sector; in this case, several servo sectors need to be readto determine the complete track-ID. In this specification, the termtrack-ID is meant to include each of these possible designs.

Servo bursts are used to center the slider on the magnetically writtendata tracks. The servo bursts are used to create a position error signalused by the controller to make fine adjustments to the slider positionand center it over a track. The servo burst can be: (i) an ABCD servoburst as demonstrated in U.S. Pat. No. 6,490,111 FIG. 4; (ii) acheckerboard servo burst as demonstrated in U.S. Pat. No. 6,643,082 FIG.10 and U.S. Pat. No. 7,706,092 FIGS. 6 and 7; or (iii) a phase servoburst as demonstrated in the '581 FIG. 9 item 804. The '581 isincorporated herein by reference. The servo burst can be written witheither a single magnetic polarity or with an alternating polarity asdemonstrated in the '871. The read back signal of a servo burst willshow a repeating series of isolated pulses generated from each magnetictransition. Checkerboard servo bursts with alternating polarity areoften called DC-free null servo burst. Unlike the ABCD servo burst andcheckerboard servo bursts, the phase servo bursts are configured with aslope. There is often not a one to one correspondence between the radialdimensions of track-IDs and the servo burst. The signal magnitude of aservo burst read back is typically used by the disk drive systemelectronics to identify a fraction of track-ID's width. Data tracks areusually identified by a combination of the servo data taken from a readback of the track-ID, servo burst strength, and/or RRO value. There isoften not a one to one correspondence between the radial dimensions of aservo burst and a data track.

RRO values are determined usually during manufacturing and stored withinthe disk drive system for use during operation. If the RRO values arestored within the servo sectors, they are often stored as bits ofinformation located after the servo burst.

Often there is a pad before and/or after the servo data. The pad doesnot necessarily include any specific data. The pad is used toaccommodate read-to-write and write-to-read transition timing of thewrite driver, read signal preamplifier, and read-write channel.

Patterned magnetic disk designs have emerged recently to enhance therecording density by providing better track and/or bit isolation. Forexample, nano scale non-magnetic grooves may be patterned on themagnetic disk by removing magnetic material and leaving behind discretetracks or bit “islands” of magnetic material. There are two common formsof patterned magnetic disk: Discrete Track Media (“DTM”) and BitPatterned Media (“BPM”). In DTM, discrete tracks are patterned into themagnetic disk and data bits are magnetically written thereto. In BPM,individual bits may be patterned via track grooves and crossing bitgrooves, creating islands of magnetic material. Both BPM and DTMestablish data patterns where data may be magnetically written. Readback of pattern media will show magnetic transitions between themagnetized magnetic islands and non-magnetic grooves, such as in BPM;read back of pattern media will also show magnetic transitions occurringwithin a single magnetic island, such as in DTM. (Note that, unlike DTMor BPM, conventional non-patterned media has layers of magnetic materialsputtered onto the entire front and back surfaces of the magnetic diskand there are typically no pre-formatted patterns).

In both BPM and DTM the disk patterning process can be used to createunique magnetic islands in the shape of various portions of the servodata. In U.S. Pat. No. 6,490,111 (“the '111”) FIG. 4, for example, thepattern imprint includes magnetic islands in the shape of all theintended final servo data, including the gray code track-ID. With the'111 design, the servo data is readable by the read head after bulkDirect Current (“DC”) magnetization (e.g., single magnetic polarity) ofthe magnetic islands because of the read back signal contrast betweenthe presence and absence of magnetic material. The problem with thisservo data writing approach, however, is that many of the availableplanarization constraints have difficulty dealing with the widelyvarying sizes and shapes of the gray code track-ID formats and sector-IDformats. Certain planarization constraints impose design rules onpatterned magnetic disk. For liquid-based planarization, allnon-magnetic grooves should be configured at or below a specified widththat allows for the liquid to planarize the grooves through capillaryforces. For dry planarization, such as vacuum deposit/etchbackplanarization, the ratio of magnetic island widths to non-magneticgroove widths needs to be constant everywhere (“Dry Planarization DesignRule #1”). It is also advantageous to ensure that magnetic island andnon-magnetic groove widths are constant everywhere (“Dry PlanarizationDesign Rule #2”). Servo patterns that comply with these planarizationconstraints are sometimes called planarization compatible servo (“PCS”)or planarization-compatible servo pattern (“PSP”).

An alternative approach to bulk DC magnetization of pre-patterned graycode track-ID, is to hard pattern only a portion of the servo data onthe magnetic disk and fill in the remaining servo data by magneticallywriting with the write head the desired servo data into the remainingportions of the servo pattern. This process has been called assistedservo track write for patterned media. In the '581, for instance, theservo pattern includes a single servo write assist pattern and aplurality of checkerboard sub-patterns. The servo write assist patternis comprised of radial magnetic islands and radial non-magnetic grooves.The servo write assist pattern can also, as demonstrated in FIG. 6 ofthe '111, be comprised of circumferential magnetic rows andcircumferential non-magnetic grooves. After assembly of the patternedmagnetic disk into a disk drive system, the write head is used tomagnetically write the track-ID in the servo write assist patterns. Thewriting of the track-ID by the write head does not change the shape ofthe magnetic islands and non-magnetic grooves of the servo write assistpatterns.

A hybrid servo writing approach is to combine of small number ofbootstrap patterns (which are operable after DC magnetization) andpredominant servo write assist patterns (which require magnetic writingby the write head). The bootstrap patterns may include pre-patterned SAMpatterns, gray code track-ID patterns, sector-ID patterns, and burstpatterns that do not comply with the planarization constraints. Thebootstrap patterns may be designed to comply with planarizationconstraints by using phase patterns (e.g., chevrons), such as shown inFIGS. 4A, 4B, 8, and 10 of the '240. With either pre-patterned gray codeor phase patterns, the bootstrap patterns are operational after bulk DCmagnetization of the magnetic disk. The bootstrap patterns are typicallylocated at the inner diameter of the magnetic disk and used for trackfollowing during the servo track writing of an initial set of servowrite assist patterns by the write head. After the initial set of servowrite assist patterns have been written by the write head using thebootstrap patterns for track following, additional servo write assistpatterns can be written by the write head by track following on thisinitial set. The servo write assist patterns comply with theplanarization constraints. See, for example: U.S. patent applicationSer. No. 12/800,300 FIGS. 4 and 5; and the '581 FIGS. 3, 5, 8, and 9.These references, however, do not address how best to write servo dataacross servo zone boundaries. Accordingly, there exists a need toprovide a zoned servo architecture that enables robust servo writingbeyond the writing of initial servo data, particularly addressing theneed to write servo data across servo zone boundaries.

SUMMARY

Embodiments described herein provide for patterned media concentriczones with an alternating series of concentric servo zones and overlapzones. The overlap zones facilitate the writing of servo data betweenservo zones of different servo frequency. In one embodiment, the overlapzones are dual frequency zones. The dual frequency zones have a firstset of overlap patterns with the substantially identical pattern as thebordering lower frequency servo zone and a second set of overlappatterns with the substantially identical pattern as the borderinghigher frequency servo zone. A bootstrap zone can be included near theinner diameter to assist initial servo writing. In another embodiment,the overlap zones are bootstrap zones. All bootstrap zones have bothbootstrap patterns and overlap patterns, the overlap patterns have thesubstantially identical pattern as a bordering servo zone. Bootstrappatterns only require DC magnetization for servo operability. If thebootstrap patterns do not comply with planarization constraints, theirshort radial and circumferential length prevents significant disruptionto flight of the slider over the magnetic disk. The bootstrap patternsmay also be designed to comply with planarization constraints by usingphase patterns; multiple phase patterns can provide a substitutetrack-ID pattern. The overlap patterns require the writing of servo datawithin the overlap patterns using the write head for servo operability,but overlap patterns comply with the planarization constraints. Theradial overlap length of the overlap zones are set to be greater thanthe RWO. The overlap zones can include extended sync patterns that arepaired with data sync patterns in a bordering servo zone.

For the dual frequency zone embodiment, the servo patterns and overlappatterns may be arranged in servo sectors that propagate from the innerdiameter of the magnetic disk to the outer diameter (e.g., either in anarcuate or generally straight fashion). In the overlap zones, theseservo sectors can be alternating frequencies. The odd servo sectors, forinstance, can include lower frequency overlap patterns while the evenservo sectors can include higher frequency overlap patterns. The overlappatterns can be the substantially identical pattern as the borderingservo zones and/or the substantially identical servo frequency.

The radial overlap length of the overlap zones can accommodate the RWOof the slider. As discussed, the RWO changes with the slider's angularposition over the magnetic disk based on the location of the read headand write head on the slider and the arc made by the actuator over themagnetic disk. The radial overlap length of the overlap zones can beadaptable such that the radial overlap length of each overlap zone islong enough to accommodate the maximum RWO in each overlap zone. Theradial overlap length can also be some multiple of the maximum RWO foreach overlap zone to accommodate manufacturing tolerances. To simplifythe magnetic disk pattern design, the radial overlap length of theoverlap zones can be a fixed length that is greater than the maximum RWOfor all the overlap zones of the entire magnetic disk.

The overlap zones can also include extended sync patterns. The extendedsync patterns can be read by the read head when the write head ispassing over data patterns located outside the overlap zones. The readhead signal establish data clock synchronization that is used toestablish the correct write head signal frequency. The extended syncpatterns can immediately follow the overlap patterns. These extendedsync patterns therefore add further data capacity to the magnetic disk.The servo zones bordering the overlap zones may be subdivided intosub-zones with different data frequencies. E.g., each servo zone mayhave multiple sub-zones with each sub-zone having its own datafrequency.

The maximum radial length of each servo zone is a function of theplanarization constraints and the geometry of the magnetic disk. E.g.,the circumference changes less with each additional centimeter of radiusat the outer diameter of the magnetic disk when compared to the changein circumference near the inner diameter.

Each of the above embodiments may be implemented with a disk drivesystem and used to facilitate servo writing to the magnetic disk. Insome embodiments, methods also provide for servo writing based on thepatterned magnetic disk embodiments. Other exemplary embodiments may bedescribed below.

DESCRIPTION OF THE DRAWINGS

Some embodiments of the present invention are now described, by way ofexample only, and with reference to the accompanying drawings. The samereference number represents the same element or the same type of elementon all drawings.

FIG. 1 illustrates a disk drive system in an exemplary embodiment.

FIG. 2 illustrates a magnetic disk with a bootstrap zone and analternating series of concentric servo zones and overlap zones in anexemplary embodiment.

FIG. 3 illustrates the detailed view of the boundary area betweenpatterns with different frequencies in an exemplary embodiment.

FIG. 4 illustrates a block diagram of two servo zones bordering anoverlap zone in an exemplary embodiment.

FIG. 5 illustrates a detailed view of the boundary area between patternswith different frequencies in a second exemplary embodiment.

FIG. 6 illustrates alternating servo zones and dual frequency zonesalong with a bootstrap zone at the inner diameter of the magnetic diskin an exemplary embodiment.

FIGS. 7A and 7B illustrate a close-up view of a slider and its relativeposition over a bootstrap zone patterned at an outer diameter of themagnetic disk in an exemplary embodiment.

FIGS. 8A and 8B illustrate a close-up view of the slider and itsrelative position over a bootstrap zone patterned at a middle diameterof the magnetic disk in an exemplary embodiment.

FIGS. 9A and 9B illustrate a close-up view of the slider and itsrelative position over a bootstrap zone patterned at an inner diameterof the magnetic disk in an exemplary embodiment.

FIG. 10 illustrates alternating servo zones and bootstrap zones in anexemplary embodiment.

FIG. 11 illustrates a servo pattern in the servo zones of the magneticdisk in an exemplary embodiment.

FIGS. 12-15 illustrate exemplary embodiments of bootstrap patterns.

FIG. 16 illustrates the slider's RWO and servo writing while trackfollowing on a DC-magnetized bootstrap pattern in an exemplaryembodiment.

FIG. 17 illustrates the slider's RWO and servo writing while trackfollowing on the servo data written into an odd servo sector to writeservo data into an even servo sector.

FIGS. 18A-18C illustrate a close-up view of a slider's variable angularposition with its associated changes to RWO in an exemplary embodiment.

FIGS. 19, 20A, and 20B illustrate the variables and calculations used todetermine optimal radial dimensions of servo zones in an exemplaryembodiment.

FIG. 21 illustrates a servo zone boundary between higher and lowerfrequency servo zones with extended sync patterns that provide dataclock synchronization in an exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

The figures and the following description illustrate specific exemplaryembodiments of the invention. It will thus be appreciated that thoseskilled in the art will be able to devise various arrangements that,although not explicitly described or shown herein, embody the principlesof the invention and are included within the scope of the invention.Furthermore, any examples described herein are intended to aid inunderstanding the principles of the invention, and are to be construedas being without limitation to such specifically recited examples andconditions. As a result, the invention is not limited to the specificembodiments or examples described below, but by the claims and theirequivalents.

FIG. 1 illustrates a simplified overhead view of a typical disk drivesystem 100, which is suitable to include a magnetic disk 110, asexemplarily described herein. In the disk drive system 100, the magneticdisk 110 is rotatably mounted upon a motorized spindle 120. A slider122, having a read head 130 and a write head 140 fabricated thereon, ismounted upon an actuator 150 to “fly” above the surface of the rotatingmagnetic disk 110. The disk drive system 100 may also include acontroller 170 that controls and drives a positional voltage to a VCM108 to control the position of the actuator 150. The disk drive system100 may also include an inner diameter crash stop 160 to hold the readhead 130 and the write head 140 still at a fixed radius relative to thecenter of the magnetic disk 110. For example, the actuator 150 pivotsabout the pivot point 175 against the crash stop 160 to prevent the readhead 130 and the write head 140 from traveling past a certain point atthe inner diameter. The disk drive system 100 may include othercomponents (e.g., a spindle motor used to rotate the magnetic disk 110)that are not shown for the sake of brevity. Additionally, certaincomponents within the disk drive system 100 may be implemented ashardware, software, firmware, or various combinations thereof.

In conventional servo writing, a circular track pattern is created bypushing the actuator 150 of the disk drive system 100 against the crashstop 160 and then writing a single track pattern or a group ofconcentric track patterns at increasing radii. Once enough concentrictracks have been written, the read head 130 may sense previously writtenservo data and allow propagation of new servo tracks (e.g., both servobursts and track-ID) across the surface of the magnetic disk 110. Thatis, the read head 130 may track follow over previously written servodata while the offset write head 140 is used to write new servo dataover tracks that have not yet been servo written.

With the advent of patterned media, servo writing is presented with newchallenges. For example, track trajectory is generally not concentricwith the center of rotation of the spindle 120 because it is difficultif not impossible to concentrically align data patterns with the spindle120.

Zoned Servo

FIG. 2 illustrates one example of the magnetic disk 110 employing abootstrap zone 400 and an alternating series of servo zones 230 andoverlap zones 270. Within each of the servo zones 230, the servofrequency can be constant or can be within a range of frequencies. Aconstant servo frequency in an individual servo zone 230 enhancespredictability of the servo frequency, but the circumferential width ofthe servo patterns generally must increase proportionally to the radius.If the servo frequency is a range of frequencies, then thecircumferential width of the servo patterns can be constant within theservo zones 230. The servo frequency is generally different in eachservo zone 230 and the servo zones 230 are patterned from the innerdiameter of the magnetic disk 110 to the outer diameter according toincreasing servo frequency.

The servo zones 230 include both servo patterns and data patterns.Usually, the servo patterns are placed into predictably located servosectors and the data patterns are placed in data regions between theservo sectors. The data patterns can be arranged into one or moreconcentric sub-zones within the servo zones 230. The data frequencywithin each sub-zone can be is constant or can be within a range offrequencies. In this manner, the data frequency can be optimized withmore sub-zones while maintaining a simpler servo zone layout. The datafrequency within each sub-zone scales roughly with mean radius. The twosub-zones bordering an overlap zone can be the same frequency.

FIG. 4 illustrates the dual frequency zone embodiment. A higherfrequency servo zone 230-1 and a lower frequency servo zone 230-2 borderthe overlap zone 270-1. In the odd servo sectors 220-1 and 220-3, theoverlap zone has overlap patterns that are substantially identical to(or substantial identical servo frequency as) the servo patterns of thelower frequency servo zone 230-2. In the even servo sectors 220-2 and220-4, the overlap zone has overlap patterns that are substantiallyidentical to the servo patterns of the higher frequency servo zone230-1. To propagate the writing of servo data into the dual frequencyservo zone 270-1, the read head can track follow on the lower frequencyservo zone 230-2. Once the servo data is written into the overlappatterns of the overlap zone 270-1, the overlap patterns' servo data canbe used to propagate the servo data into the higher frequency servo zone230-1. The servo data can be propagated in the opposite radial directionby track following on the higher frequency servo zone 230-1 to writeservo data in the overlap zone 270-1 then track follow using the overlapzone 270-1 servo data to write servo data into the lower frequency servozone 230-2.

FIG. 3 illustrates the detailed view of the boundary area betweenpatterns 300 with different frequencies in an exemplary embodiment. Notethe width differences of the radial magnetic columns 301 and the nonmagnetic grooves 302 in the boundary area between patterns 300, whichresults in different servo frequencies of the two patterns. The term“radial” with respect to the columns is intended to designate anorientation of the columns in a relatively straight line from the innerdiameter of the magnetic disk 110 to the outer diameter. The actualdimensions of the radial columns may vary but generally conform to theplanarization constraints discussed above. The patterns also includeburst patterns 320 (shown here as a plurality of checkboardsub-patterns). FIG. 3 shows an embodiment in which the two patternscommence circumferentially together at the leading edge of a servosector 220.

FIG. 5 shows an alternate embodiment where the two patterns are alignedto end circumferentially together. The FIG. 5 embodiment makes possiblethe pairing of extended sync pattern and data sync patterns. Theextended sync patterns commence circumferentially after the burstpattern 320 and extends as a set radially from top to bottom of theoverlap zone 270-1. Data sync patterns in the higher frequency servozone 230-1 are paired with the extended sync patterns of the overlapzone 270-1 and create continuous radial columns. The extended syncpattern will be discussed in more detail below.

Overlap Zones can be Dual Frequency Zones

FIG. 6 illustrates alternating servo zones and dual frequency zonesalong with a bootstrap zone 400 at the inner diameter of the magneticdisk 110 in an exemplary embodiment. E.g., the overlap zones are dualfrequency zones. As with FIG. 4, the dual frequency zones 272-1-3 arebetween servo zones 230-1-4, the servo patterns and overlap patterns arelocated within servo sectors 220-1-3 on the magnetic disk 110, theoverlap patterns in the odd servo sectors 220-1 and 220-3 aresubstantially identical to (or of the substantially identical servofrequency) as the bordering lower frequency servo zone, and the overlappatterns in the even servo sector 220-2 are substantially identical to(or of the substantially identical servo frequency) as the borderinghigher frequency servo zone. In FIG. 6, a bootstrap zone 400 is locatednear the inner diameter of the magnetic disk 110. The bootstrap zone 400includes bootstrap patterns interspersed between the servo sectors220-1-3. The bootstrap patterns may also be interspersed within a subsetof the servo sectors, such as all the odd servo sectors 220-1 and 220-3.The bootstrap zone 400 also includes overlap patterns that aresubstantially identical to (or of the substantially identical servofrequency) as the bordering servo zone 230-4. Within the servo zones230-1-4, the servo frequency increases from the inner diameter of themagnetic disk 110 to the outer diameter. In this embodiment, the outerdiameter radial direction of the magnetic disk 110 is towards the servozone 230-1. Thus, the servo zone 230-1 has the highest servo frequencyin FIG. 6. The overlap patterns in the dual frequency zones 272-1-3, theoverlap patterns in the bootstrap zone 400, and the servo patterns inthe servo zones 230-1-4 comply with planarization constraints. Theregion between the servo sectors can include data patterns for a dataregion.

The bootstrap patterns in the bootstrap zone 400 may includepre-patterned SAM patterns, gray code track-ID patterns, sector-IDpatterns, and burst patterns that do not comply with the planarizationconstraints. With this pre-patterning, the bootstrap patterns areoperational after bulk DC magnetization of the magnetic disk. If thebootstrap patterns do not comply with planarization constraints, theirshort radial and circumferential length prevents significant disruptionto flight of the slider over the magnetic disk. The bootstrap patternsmay also be designed to comply with planarization constraints by usingphase patterns; multiple phase patterns can provide a substitutetrack-ID pattern, as demonstrated in FIGS. 4A, 4B, 8, and 10 of the'240. The bootstrap patterns provide a starting point for the servowrite process. The read head 130 can track follow on the bootstrappatterns to write servo data into the overlap patterns first in thebootstrap zone 400 and then into the beginning of the first servo zone230-4. To propagate the writing of servo data into the dual frequencyservo zone 270-3, the read head can track follow on the lower frequencyservo zone 230-4. Once the servo data is written into the overlappatterns of the dual frequency zone 272-3, the servo data (writtenwithin the overlap patterns) can be used to track follow while writingnew servo data into the higher frequency servo zone 230-3. The servodata can be propagated in the opposite radial direction by placing thebootstrap zone 400 at the outer diameter of the magnetic disk 110 andfollowing the same process outlined above (though in the opposite radialdirection). The servo data can also be propagated by placing thebootstrap zone somewhere between the inner and outer diameter of themagnetic disk 110 and starting the servo writing process from thisbootstrap zone. Examples of available bootstrap zone locations are shownand described in FIGS. 7-9. Examples of bootstrap patterns are shown anddescribed in FIGS. 11-15. Although shown and described with respect to acertain number of servo sectors 220, associated servo zones 230-1-4,dual frequency zones 272-1-3, and the bootstrap zone 400, the inventionis not intended to be so limited as these may be established as a matterof design choice.

FIGS. 7A and 7B illustrate a close-up view of the slider 122 and itsrelative position over a bootstrap zone 400 patterned at an outerdiameter of the magnetic disk 110 in an exemplary embodiment. FIGS. 8Aand 8B illustrate a similar view of the slider 122 and its relativeposition over a bootstrap zone 400 patterned at a middle diameter of themagnetic disk 110 while FIGS. 9A and 9B illustrate a bootstrap zone 400patterned at an inner diameter of the magnetic disk 110. Generally, thelocation of the bootstrap zone 400 depends on the configuration of readhead 130 and the write head 140 of the slider 122. For example, a slider122 configuration with the read head 130 located more toward the outerdiameter of the magnetic disk 110 generally requires that the bootstrapzone 400 be located at the outer diameter, as illustrated in FIGS. 7Aand 7B. A slider 122 configuration with the read head 130 located moretoward the inner diameter of the magnetic disk 110 generally requiresthat the bootstrap zone 400 be located at the inner diameter, asillustrated in FIGS. 9A and 9B. Bootstrap zone location in the middlediameter of the magnetic disk 110, as illustrated in FIGS. 8A and 8B arelikely less effective as the RWO near the middle diameter must beminimal and alignment tolerances would be tight.

Overlap Zones can be Bootstrap Zones

FIG. 10 illustrates alternating servo zones and bootstrap in anexemplary embodiment. E.g., the overlap zones are bootstrap zones. Aswith FIG. 6, the bootstrap zones 274-1-3 are between servo zones230-1-4, the servo patterns and overlap patterns are located withinservo sectors 220-1-3 on the magnetic disk 110, the overlap patterns inthe odd servo sectors 220-1 and 220-3 are substantially identical to (orof the substantially identical servo frequency) as the bordering lowerfrequency servo zone, and the overlap patterns in the even servo sector220-2 are substantially identical to (or of the substantially identicalservo frequency) as the bordering higher frequency servo zone. In FIG.10, an additional bootstrap zone 400 is located near the inner diameterof the magnetic disk 110. The bootstrap zone 400 includes bootstrappatterns interspersed between the servo sectors 220-1-3. (The bootstrappatterns may also be interspersed within a subset of the servo sectors,such as all the odd servo sectors). The bootstrap zones 400 include alsooverlap patterns that are substantially identical to (or of thesubstantially identical servo frequency) as a bordering servo zone 230.Within the servo zones 230-1-4, the servo frequency increases from theinner diameter of the magnetic disk 110 to the outer diameter. In thisembodiment, the outer diameter radial direction of the magnetic disk 110is towards the servo zone 230-1. Thus, the servo zone 230-1 has thehighest servo frequency in FIG. 10. The overlap patterns in thebootstrap zones 274-1-3, the overlap patterns in the bootstrap zone 400,and the servo patterns in the servo zones 230-1-4 comply withplanarization constraints. The region between the servo sectors caninclude data patterns.

The bootstrap patterns in the bootstrap zones 274-1-3 and 400 mayinclude pre-patterned SAM patterns, gray code track-ID patterns,sector-ID patterns, and burst patterns that do not comply with theplanarization constraints. With this pre-patterning, the bootstrappatterns are operational after bulk DC magnetization of the magneticdisk. If the bootstrap patterns do not comply with planarizationconstraints, but their short radial and circumferential length preventssignificant disruption to flight of the slider 122 over the magneticdisk 110. The bootstrap patterns may also be designed to comply withplanarization constraints by using phase patterns; multiple phasepatterns can provide a substitute track-ID pattern, as demonstrated inFIGS. 4A, 4B, 8, and 10 of the '240.

The bootstrap patterns provide a starting point for the servo writeprocess both at the beginning of the servo write process and betweenservo zones of different servo frequency. E.g., at the beginning of theservo write process, the read head 130 can track follow on the bootstrappatterns in the bootstrap zone 400 to write servo data into the overlappatterns first in the bootstrap zone 400 and then into the beginning ofthe first servo zone 230-4. E.g., the read head 130 can track follow onthe bootstrap patterns in the bootstrap zones 274-1-3 to write servodata into the overlap patterns first in the bootstrap zone 274-3 andthen into the beginning of the second servo zone 230-3. The servo datacan be propagated in the opposite radial direction by placing abootstrap zone at the outer diameter and following the same processoutlined above (though in the opposite radial direction). The servo datacan also be propagated by starting the servo write process at abootstrap zone somewhere between the inner and outer diameter of themagnetic disk 110. Examples of available bootstrap zone locations areshown and described in FIGS. 7-9. Examples of bootstrap patterns areshown and described in FIGS. 11-15. Although shown and described withrespect to a certain number of servo sectors 220, associated servo zones230-1-4, bootstrap zones 274-1-3 and 400, the invention is not intendedto be so limited as these may be established as a matter of designchoice.

FIG. 11 illustrates a pattern 300 that can be used as a servo pattern ina servo zone or an overlap pattern in an overlap zone. The pattern 300of this embodiment includes a plurality of radial magnetic columns 301patterned on the magnetic disk 110 separated by radial non magneticgrooves 302 (e.g., via the removal of the magnetic material between theradial magnetic columns 301). The radial magnetic columns 301 and radialnon magnetic grooves 302 define a servo write assist pattern 310 inwhich servo data may be written.

The pattern 300 also includes burst pattern 320 comprising a pluralityof magnetic islands 341 separated by non magnetic depressions 342, or“valleys”, (e.g., again via the removal of the magnetic material betweenthe magnetic islands 341). The burst pattern 320, in this embodiment,comprises a first and second checkerboard sub-pattern 321 and 322,respectively, that are radially offset by some fraction of a magneticisland dimension (e.g., between a quarter to half an island width). Thecheckerboard sub-patterns 321 and 322 may be substantially symmetric.For example, each of the checkerboard sub-patterns 321 and 322 maycomprise about the same size and number of magnetic islands 341. Theinvention, however, is not intended be limited to the checkerboardsub-patterns 321 and 322 exemplary embodiment as other types of burstpatterns may be employed. For example, an ABCD pattern can be configuredwith four sub-patterns, such as with the A & B patterns at the locationof the sub-pattern 321 and the C & D patterns at the location of thesub-patterns 322. Alternatively, the burst pattern 320 may be configuredwith three or four roughly equal sized checkerboard sub-patterns witheach being radially offset to one another by some fraction of a magneticisland dimension.

The pattern 300 also includes a pad pattern 351 comprising a number ofradial magnetic columns 301 and radial non magnetic grooves 302. The padpattern 351 may be used as a read-to-write timing delay buffer betweenthe pattern 300 and subsequent data patterns. Alternatively oradditionally, the pad pattern 351 may be used to write additional servodata such as RRO values. The physical dimensions and spacings of theradial magnetic columns 301 in the pad pattern 351 may be different fromthe magnetic column 301 dimensions elsewhere in the pattern 300.

FIGS. 12-15 illustrate exemplary bootstrap patterns that may bepatterned on the magnetic disk 110. As mentioned, the bootstrap patternhas servo data pre-patterned into the magnetic disk 110 to facilitatesubsequent servo writing. The bootstrap patterns may includepre-patterned servo sync patterns, SAM patterns, gray code track-IDpatterns, sector-ID patterns, and burst patterns that do not all complywith the planarization constraints. With this pre-patterning, thebootstrap patterns are operational after bulk DC magnetization of themagnetic disk 110.

In FIG. 12, much of the bootstrap pattern 550 does not comply withplanarization constraints. The 552 area for instance can include SAMpatterns, gray code track-ID patterns, and sector-ID patterns that areirregular in shape and do not comply with planarization constraints. Theburst pattern 553 can be designed in a checkerboard pattern that is morelikely to comply with planarization constraints. In FIG. 12 there arefour checkboard sub-patterns but two or three sub-patterns can also beused. The servo sync pattern 551 and pad pattern 554 (which include aplurality of radial magnetic columns 301 and radial non magnetic grooves302) can more easily comply with planarization constraints due to theirrepetitive pattern. The bootstrap pattern 550 is operational after bulkDC magnetization of the magnetic disk 110.

FIG. 13 illustrates another bootstrap pattern 600 with an ABCD pattern607. In this embodiment, a series of radial magnetic columns 301 andradial non magnetic grooves 302 provide a servo sync pattern 604, a SAMpattern 605, a gray code track-ID pattern 606, and an ABCD pattern 607.The bootstrap pattern 600 is operational after bulk DC magnetization ofthe magnetic disk.

Bootstrap patterns 650 and 700 (of FIGS. 14 and 15, respectively) aredesigned to better comply with the planarization constraints. In each ofthese embodiments, the bootstrap patterns 650 and 700 are configuredwith phase patterns. FIG. 14 has sets of radial magnetic columns 654bookending the phase patterns. The phase patterns have magnetic columns651 and non magnetic grooves 652 which make acute angles to the radialdirection and look like chevrons. The sets of radial magnetic columns654 at the start the bootstrap pattern 650 can function as a SAMpattern. The phase patterns of FIG. 14 can be used similar to otherburst patterns (such as ABCD patterns or checkerboard sub-patterns) todetermine fractions of a track width. FIG. 15 is illustrated with fivesets of phase patterns, which provide additional track-ID servo data,similar to the use of gray code track-ID patterns. See FIGS. 4A, 4B, 8,and 10 of the '240 for alternative designs.

FIGS. 16 and 17 illustrate servo writing via a bootstrap pattern 550 inan exemplary embodiment. In this embodiment, the bootstrap pattern 550has pre-patterned servo sync patterns and SAM patterns 559, sector-IDand track-ID patterns 552, checkboard sub-patterns 553, and a padpattern 554. The SAM pattern, sector-ID pattern, and the track-IDpattern need not comply with planarization constraints. With thispre-patterning, the bootstrap patterns are operational after bulk DCmagnetization of the magnetic disk 110. The bootstrap pattern 550 may bepatterned within a bootstrap zone 400 near the inner diameter of themagnetic disk 110, as illustrated in FIG. 6. The bootstrap pattern 550may also be patterned within any of the bootstrap zones illustrated inFIG. 10 items 270-1-3 and 400. In both FIGS. 6 and 10, the bootstrapzone 400 near the inner diameter of the magnetic disk 110 includes bothbootstrap patterns and overlap patterns. During servo writing, the readhead 130 on the slider 122 can track follow on the bootstrap patterns550 (that have been DC magnetized) and write servo data into thepatterns 300 of servo sectors 220 using the write head 140 on the slider122. As illustrated in FIG. 17, the read head 130 can track follow onthe servo data previously written into the pattern 300 of an odd servosector 220-1 to write servo data into the pattern 300 of an even servosector 220-2 using the write head 140 on the slider 122. The servosectors 220 may alternate between “odd” and “even” as demonstrated inFIGS. 6 and 10. The drive electronics interpret the slider's 122position from the read signal from the read head 130, adjusts theposition of the slider 122 over the magnetic disk 110, and controls thewrite signal to the write head 140. Note that the RWO between the readhead 130 and the write head 140 results in the writing of servo datainto a different track than the track that is read for track following.This RWO allows the controller 170 to stepwise propagate the servo datawriting from the inner diameter of the magnetic disk 110 to the outerdiameter by track following on previously written servo data read by theoffset read head 130.

Radial Overlap Lengths of Overlap Zones

It is likely desirable to not place user data within the overlap zones.Bootstrap patterns, for instance, are place between servo sectors (aregion normally reserved for user-data) and would likely disrupt thenormal data layout architecture. Dual frequencies, for instance, wouldcreate greater complexity for the servo control electronics. Thisincreased complexity may only be manageable during the servo writingprocess at the manufacturing site where additional processing power andtime can be allocated. If no data is placed into the overlap zones, lessreal estate is available on the magnetic disk 110 for data patterns. Toavoid substantial losses to data capacity for the magnetic disk 110, theradial overlap length of the overlap zones can be minimized A primaryfactor for the radial overlap length of the overlap zones is the RWO.

In the FIG. 6 embodiment, the overlap zones are dual frequency zones. Inthe FIG. 10 embodiment, the overlap zones are bootstrap zones. For bothembodiments, a first set of servo data is read for track following towrite a second set of servo data. In the dual frequency zones, servodata is first written to the first set of overlap patterns (such as thelower frequency overlap patterns of the odd servo sectors 220-1 and220-3) then used for track following to write servo data into the secondset of overlap patterns (such as the higher frequency overlap patternsof the even servo sectors 220-2). In the bootstrap zone embodiment ofFIG. 10, the bootstrap patterns (after DC magnetization) are used fortrack following to write the overlap patterns. In either embodiment,aggressive decreases to the radial overlap length of the overlap zonemay at some point result in reliability issues during the servo writingprocess. Sliders with larger RWO will likely require overlap zones withlonger radial overlap lengths and sliders with smaller RWO will likelyenable overlap zones with shorter radial overlap lengths.

In one embodiment, all the overlap zones 270 may be configured with aradial distance that is at least greater than or equal to the maximumRWO 902 of the slider 122 for all radial locations of the magnetic disk110. For the rough dimensions shown in FIGS. 18A-C, the radial overlaplength of every overlap zone would be greater than or equal to the RWOof FIG. 18C. A substantially constant radial overlap length for everyoverlap zone can simplify the design of the magnetic disk 110, but couldreduce slightly the data capacity of the disk drive device 100. Asubstantially constant radial length can be used on just one side ofeach magnetic disk 110 or both sides of each magnetic disk 110. Thesubstantially constant radial overlap length should be greater than themaximum RWO for any of the overlap zones 270 on each side of themagnetic disk 110 and/or on both sides of the magnetic disk 110. In analternative embodiment, the radial overlap length of each overlap zone270 may be individually configured based on the RWO at the radius ofeach overlap zone. For example considering FIGS. 18A-C, the overlapzones 270 closer to the inner diameter of the magnetic disk 110 may beconfigured with shorter radial overlap lengths than the overlap zones270 that are nearer the outer diameter.

Radial Lengths of Servo Zones

Another consideration regarding the layout of servo zones 230 andoverlap zones 270 involves the geometry of the magnetic disk 110. Nearthe inner diameter, for instance, the circumference of a track willdouble when the radius increases from one centimeter to two centimeters.Near the middle diameter of the magnetic disk 110, the circumference ofa track will only increase 50% when the radius increases from twocentimeters to three centimeters. Near the outer diameter of themagnetic disk 110, the circumference of a track will only increase by25% when the radius increases from four centimeters to five centimeters.If the planarization constraints allow a maximum 25% deviation within aservo zone 230, then near the outer diameter of the magnetic disk 110the maximum servo zone 230 radial length can be about one centimeter.However, near the inner diameter of the magnetic disk 110, a maximum 25%deviation would limit the maximum servo zone 230 radial length to about2.5 milimeters. Near the middle diameter of the magnetic disk 110, amaximum 25% deviation would limit the maximum servo zone 230 radiallength to about five millimeters.

FIG. 19 illustrates the magnetic disk 110 with radial dimension and zonefrequency considerations of servo zones 230 that are used to computeservo zone radial lengths in an exemplary embodiment. For example, thedesign parameters used in constructing the servo patterns include theservo frequency f_(i) (i=1 . . . n, where n is simply used herein as aninteger greater than 1, but not to designate actual frequency) of theservo zone 230 based on its radial dimension r_(i) (i=0 . . . n) on themagnetic disk 110.

To conform to the various planarization constraints described above(e.g., the Dry Planarization Design Rules #1 and #2), the widths of datatracks and/or non magnetic grooves separating those tracks may increase(e.g., increased track pitch, T_(p)). A similar consideration is thechanging “pitch” of the servo patterns within the servo zones 230. Inthis regard, the maximum circumferential pitch difference may becalculated as (maximum C_(p)−minimum C_(p)). Other factors to considerare the number of zones n on the magnetic disk 110, the revolution N ofthe magnetic disk 110, the innermost radius r₀ of the magnetic disk 110,and the outermost radius r_(n) of the magnetic disk 110. Generally, tocomply with planarization constraints, the preamble pitch of a servopattern is configured as C_(p)=2πrN/f, where the minimum circumferentialpitch C_(p) value is same for each servo zone 230 and the maximumcircumferential pitch C_(p) value is same for each servo zone 230. Toconform to the land/groove dimension ratios of the Dry PlanarizationDesign Rule #1 at data and servo zones, boundary conditions for theservo zones 230 are generally configured as the minimum C_(p)=T_(P),which provides suitable fly high control of the slider 122. In thisregard, the maximum C_(p)=T_(p) and [(maximum C_(p))−(minimumC_(p))]/2+(minimum C_(p))=T_(p).

With these concepts in mind, the following mathematical relationshipsmay exist (e.g., without yet considering the overlap zones 270):

${C_{p}\left( {f,r} \right)} = \frac{2\pi \; {rN}}{f}$$\frac{r_{0}}{f_{1}} = {\ldots = {\frac{r_{i - 1}}{f_{i}} = {\ldots = {\frac{r_{n - 1}}{f_{n}} = {\frac{\min \; C_{p}}{2\pi \; N} = \frac{T_{p}}{2\pi \; N}}}}}}$$\frac{r_{1}}{f_{1}} = {\ldots = {\frac{r_{i}}{f_{i}} = {\ldots = {\frac{r_{n}}{f_{n}} = \frac{\max \; C_{p}}{2\pi \; N}}}}}$$r_{i} = \left( {r_{0}^{n - i}r_{n}^{i}} \right)^{\frac{1}{n}}$$f_{i} = {{\frac{2\pi \; N}{T_{p}}r_{i - 1}} = {\frac{2\pi \; N}{T_{p}}\left( {r_{0}^{n - i + 1}r_{n}^{i - 1}} \right)^{\frac{1}{n}}}}$and${\max \; C_{p}} = {{2\pi \; N\frac{r_{i}}{f_{i}}} = {{\frac{r_{i}}{r_{i - 1}}T_{p}} = {\left( \frac{r_{n}}{r_{0}} \right)^{\frac{1}{n}}T_{p}}}}$

When the overlap zones 270 of the servo zones 230 comprise a length 2l,boundary conditions are the minimum C_(P)=T_(p), with the minimum C_(P)being same value for each zone servo zone 230. From this, the followingmay be computed:

$\frac{r_{0}}{f_{1}} = {\ldots = {\frac{r_{i - 1} - l}{f_{i}} = {\ldots = {\frac{r_{n - 1} - l}{f_{n}} = {\frac{\min \; C_{p}}{2\pi \; N} = \frac{T_{p}}{2\pi \; N}}}}}}$

The maximum C_(P) is also same value for each servo zone 230 and can becomputed as follows:

$\frac{r_{1} + l}{f_{1}} = {\ldots = {\frac{r_{i} + l}{f_{i}} = {\ldots = {\frac{r_{n}}{f_{n}} = \frac{\max \; C_{p}}{2\pi \; N}}}}}$

Simple solutions to the sizing and pitch considerations of the servozones 230, the servo patterns therein, and the overlap zones 270 do notgenerally exist. However, these may be characterized in the followingpattern 300 and graph 950 illustrated in FIGS. 20A and 20B respectively.The graph 950 illustrates the changing pitch and radial dimension of thepattern 300 based on its particular location on the magnetic disk 110(e.g., within a particular servo zone 230). In FIG. 20B, a bootstrapzone (Zone-B) and a series of alternating servo zones 230 (odd numberedzones) and overlap zones 270 (even numbered zones) are configured fromthe inner diameter of the magnetic disk 110 to the outer diameteraccording to increasing frequency. In this instance, Zone B isconfigured closest to the inner diameter the magnetic disk 110 followedby the servo zone 230 labeled “Zone 7”, having the lowest servofrequency in this example. In similar fashion, the servo zone 230labeled “Zone 1” is configured closest to the outer diameter of themagnetic disk 110 and has the highest servo frequency in this example.Assuming that each of the servo zones is configured with the pattern 300of FIG. 20A, the graph 950 provides an insight as to how the pattern 300may increase in radial dimension and pitch based on its location withinhigher frequency servo zones 230. Similar insight can be gained from thegraph 950 into the overlap zones 270. While certain dimensions for aparticular servo pattern on a magnetic disk are illustrated in the graph950, the invention is not intended to be limited to any particulardimension or servo pattern. The graph 950 is merely intended to provideone manner in which zoned servo may be sized and implemented.

Extended Sync Patterns

FIG. 21 illustrates a boundary area between patterns 300-1 and 300-2wherein the overlap zone 270 has extended sync patterns. In the servozone 230-1, pattern 300-1 has a burst pattern 320-1, a pad pattern351-1, and a data sync pattern (on the leftward portion of the dataregion 240-1 a). In the servo zone 230-2, pattern 300-2 has a burstpattern 320-2, a pad pattern 351-2, and a data sync pattern (on theleftward portion of the data region 240-2). Servo zone 230-1 has ahigher servo frequency than the servo zone 230-2. Between the servozones 230-1 and 230-2 is an overlap zone 270 with an extended syncpattern (on the leftward portion of the data region 240-1 b) that issubstantially identical in frequency as the data sync pattern in dataregion 240-1 a. Note that, as in FIG. 5, the pad patterns 351-1 and351-2 end circumferentially at trailing edge of the servo sectors 220;in this manner, pairs of the extended sync patterns of the overlap zone270 and the data sync patterns in the higher frequency servo zone 230-1commence circumferentially together along the trailing edge of the servosectors 220 and align into a set of radial columns. Eg, the servopatterns and the overlap patterns are not aligned necessarily at theleading edge of the servo sectors 220 but are aligned at the trailingedge of the servo sector such that pairs of extended sync patterns anddata sync patterns commence circumferentially together as a pair at thetrailing edge of the servo sector.

The extended sync pattern enables the read head 130 (which has RWO fromthe write head 140) to acquire data clock synchronization for writingdata in the data region 240-1 a. The overlap zone 270 also has overlappatterns that are substantially identical to the servo patterns in servozone 230-2. Data region 240-1 has a higher frequency than the dataregion 240-2. As previously mentioned, the overlap zones 270 aregenerally not used for user data, so the data patterns would normally belimited to data regions 240-1 a and 240-2 of FIG. 21. However, toincrease data capacity of the magnetic disk 110, the overlap zones 270can include data patterns, such as in the data region 240-1 b of FIG.21. There may be pairs of extended sync patterns and data sync patternsbetween the servo sectors 220, as many of the data blocks commencebetween the servo sectors in typical disk drive device data regionlayouts and/or are split in two by the servo sectors 220.

Although specific embodiments were described herein, the scope of theinvention is not limited to those specific embodiments. The scope of theinvention is defined by the following claims and any equivalentsthereof.

1. A disk drive system comprising: (a) one or more magnetic disksmounted on a spindle motor, a plurality of concentric zones comprisingan alternating series of servo zones and overlap zones, wherein theservo frequency of each servo zone is different from the servo frequencyof the other servo zones, wherein the servo zones are patterned from theinner diameter of the one or more magnetic disks to the outer diameteraccording to increasing servo frequency, wherein each servo zonecomprises a plurality of servo patterns, wherein each overlap zonecomprises a plurality of overlap patterns, and wherein each overlap zonehas a radial overlap length; and (b) an actuator comprising a pivotpoint and at least one slider, wherein each slider has a read head and awrite head, wherein each slider has a radial read-write offset length(RWO) that varies with the radial position of the slider, wherein eachslider has a maximum RWO within each overlap zone, and wherein theradial overlap length of each overlap zone is greater than the maximumRWO for that overlap zone.
 2. The disk drive system of claim 1, whereinthe radial overlap lengths vary from the inner diameter of the magneticdisk to the outer diameter.
 3. The disk drive system of claim 2, whereinthe radial overlap lengths generally decrease in radial length from theinner diameter of the magnetic disk to the outer diameter.
 4. The diskdrive system of claim 2, wherein the radial overlap lengths generallyincrease in radial length from the inner diameter of the magnetic diskto the outer diameter.
 5. The disk drive system of claim 2, wherein theradial overlap lengths generally decrease in radial length from a middlediameter of the magnetic disk to the inner diameter, and wherein theradial overlap lengths generally increase in radial length from themiddle diameter to the outer diameter.
 6. The disk drive system of claim2, wherein the radial overlap length of each overlap zone is greaterthan twice the maximum RWO for that overlap zone.
 7. The disk drivesystem of claim 1, wherein, for each of the overlap zones on one side ofeach magnetic disk, the radial overlap lengths are substantiallyconstant from the inner diameter of the magnetic disk to the outerdiameter.
 8. The disk drive system of claim 7, wherein the constantradial overlap length on one side of each magnetic disk is greater thanthe maximum RWO for any of the overlap zones for that side of themagnetic disk.
 9. The disk drive system of claim 7, wherein the constantradial overlap length on one side of each magnetic disk is greater thantwice the maximum RWO for any of the overlap zones for that side of themagnetic disk.
 10. The disk drive system of claim 1, wherein, for eachof the overlap zones on both sides of each magnetic disk, the radialoverlap lengths are substantially constant from the inner diameter ofthe magnetic disk to the outer diameter.
 11. The disk drive system ofclaim 10, wherein the constant radial overlap length on both sides ofeach magnetic disk is greater than the maximum RWO for any of theoverlap zones for that magnetic disk.
 12. The disk drive system of claim10, wherein the constant radial overlap length on both sides of eachmagnetic disk is greater than twice the maximum RWO for any of theoverlap zones for that magnetic disk.
 13. The disk drive system of claim1, wherein the overlap patterns in each overlap zone are patterned withthe substantially identical pattern as the servo patterns of thebordering lower frequency servo zone.
 14. The disk drive system of claim1, wherein the overlap patterns in each overlap zone are patterned withthe substantially identical pattern as the servo patterns of thebordering higher frequency servo zone.
 15. The disk drive system ofclaim 1, wherein the overlap patterns in each overlap zone are patternedwith the substantially identical frequency as the servo patterns of thebordering lower frequency servo zone.
 16. The disk drive system of claim1, wherein the overlap patterns in each overlap zone are patterned withthe substantially identical frequency as the servo patterns of thebordering higher frequency servo zone.
 17. The disk drive system ofclaim 1, wherein the overlap patterns in each overlap zone comprise afirst and second subset, wherein the first subset is patterned with thesubstantially identical pattern as the servo patterns of the borderinglower frequency servo zone, and wherein the second subset is patternedwith the substantially identical pattern as the servo patterns of thebordering higher frequency servo zone.
 18. The disk drive system ofclaim 1, wherein the overlap patterns in each overlap zone comprise afirst and second subset, wherein the first subset is patterned with thesubstantially identical frequency as the servo patterns of the borderinglower frequency servo zone, and wherein the second subset is patternedwith the substantially identical frequency as the servo patterns of thebordering higher frequency servo zone.
 19. The disk drive system ofclaim 1, wherein the overlap patterns in each overlap zone arecircumferentially aligned with the servo patterns in the bordering lowerfrequency servo zone.
 20. The disk drive system of claim 1, wherein theoverlap patterns in each overlap zone are circumferentially aligned withthe servo patterns in the bordering higher frequency servo zone.
 21. Thedisk drive system of claim 1, wherein the servo zones generally increasein radial length from the inner diameter of the magnetic disk to theouter diameter.
 22. The disk drive system of claim 1, wherein, withineach servo zone, the servo patterns comprise radial magnetic columns andradial non-magnetic grooves having widths that establish servo frequencyfor the servo zone.
 23. The disk drive system of claim 22, wherein theoverlap zones are comprised of a plurality of bootstrap patterns, andwherein the bootstrap patterns are patterned between the servo sectorswithin each overlap zone.
 24. The disk drive system of claim 22, whereinthe overlap zones are comprised of a plurality of bootstrap patterns andoverlap patterns, and wherein the bootstrap patterns are patternedwithin alternating servo sectors of each overlap zone.